This invention generally relates to methods and apparatus for manufacturing slider-operated flexible zippers for use in reclosable pouches, bags or other packages of the type in which material, such as foodstuff and detergent, are stored.
Reclosable bags are finding ever-growing acceptance as primary packaging, particularly as packaging for foodstuffs such as cereal, fresh vegetables, snacks and the like. Such bags provide the consumer with the ability to readily store, in a closed, if not sealed, package any unused portion of the packaged product even after the package is initially opened. To gain acceptance as a primary package for foodstuffs, it is virtually mandatory that the package exhibit some form of tamper evidence to protect the consumer and maintain the wholesomeness of the contained product. In addition, in many cases it is necessary that food product be hermetically packaged.
Reclosable fastener assemblies are useful for sealing thermoplastic pouches or bags. Such fastener assemblies often include a plastic zipper and a slider. Typically, the plastic zippers include a pair of interlockable profiled members that form a closure. As the slider moves across the profiles, the profiles are opened or closed. The profiles in plastic zippers can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure members, etc. Reclosable bags having slider-operated zippers are generally more desirable to consumers than bags having zippers without sliders because the slider eliminates the need for the consumer to align the interlockable zipper profiles before causing those profiles to engage.
In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction. Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures, portions of which form a fulcrum about which the profiled structures may be pivoted out of engagement when lower edges of the bases are forced towards each other.
One of the important features of such reclosable fastener assemblies is the end stop, which prevents the slider from falling off when the slider reaches the end of the fastener. A slider end stop is provided on each end of the zipper. End stops have taken on various configurations, such as, for example, riveted end clamps such as those described in U.S. Pat. Nos. 5,067,208 and 5,161,286; transverse end stops made from molten material of the fastener strips, as described in U.S. Pat. No. 5,088,971; reciprocating anvils, as described in U.S. Pat. No. 5,131,121; tubular end stops, as described in U.S. Pat. No. 5,405,478; a window structure combined with sealed zipper ends, as described in U.S. Pat. No. 5,442,837; or plastic end clips fused to the zipper as described in U.S. Pat. No. 5,448,807.
U.S. Pat. No. 5,950,285 discloses a reclosable bag having end stops designed to prevent a slider from being pulled off the end of the zipper. The end stops are formed from the material of the zipper profiles and “rise vertically” from the zipper for the purpose of blocking further movement of the slider. The end stops are formed by first aligning together the opposing profiles at an end stop area proximate to an end of the bag, and then fusing the zipper profiles at the end stop area to provide a vertical structure, while at the same time keeping the base of the profiles intact so that the slider cannot lift off of the zipper in the parked position. Preferably, the profiles are fused by directing ultrasonic energy to the end stop areas.
A slider end stop must be designed to withstand the force applied by a consumer during normal use. More specifically, as the consumer pulls the slider to either end of the zipper, the end stop should not bend, fold, collapse or otherwise lose its ability to stop the slider when the slider is pressed against the end stop with the pulling force being exerted by the consumer. Preferably a slider end stop has relatively high slider pull-off resistance.
There is a need for improvements in the manufacture and construction of slider end stops for slider-operated zippers. In particular, there is a need for an improved, yet economical method of making a slider end stop having high slider pull-off resistance.